Two-Dimensional Sheet Stabilized Emulsion Based Inks

ABSTRACT

The present disclosure provides advantageous sheet stabilized emulsion based inks, and improved methods for fabricating and using such inks. More particularly, the present disclosure provides improved methods for fabricating conductive inks derived from water-in-oil emulsions stabilized by sheets exfoliated from layered materials (e.g., substantially pristine and non-oxidized graphite or hexagonal boron nitride), and related methods of use. A layered material (e.g., substantially pristine and non-oxidized graphite or hexagonal boron nitride) can be exfoliated into individual sheets, and these sheets can be utilized to stabilize water-in-oil emulsions. In certain embodiments, by utilizing long chain alkanes (e.g., hexadecane), one can advantageously fabricate emulsions with high viscosity and stability. In this form, the emulsions can be used as inks, thereby advantageously providing an inexpensive route to printing electrically conducting and/or insulating lines and shapes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Applicationentitled “Two-Dimensional Sheet Stabilized Emulsion Based Inks,” whichwas filed on Nov. 1, 2017, and assigned Ser. No. 62/580,214, thecontents of which are herein incorporated by reference in theirentirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

This invention was made with government support under Grant #DMR1535412awarded by the National Science Foundation. The government has certainrights in the invention.

FIELD OF THE DISCLOSURE

The present disclosure relates to sheet stabilized emulsion based inksand related methods of use and fabrication and, more particularly, toconductive inks derived from water-in-oil emulsions stabilized by sheetsexfoliated from layered materials (e.g., substantially pristine andnon-oxidized graphite or hexagonal boron nitride), and related methodsof fabrication.

BACKGROUND OF THE DISCLOSURE

In general, flexible displays and wearable sensors can requireconductive materials that are able to bend and deform without crackingor breaking. Some potential and current applications include, forexample, electronic and wearable textiles, 3D antennas and conformalprinting, electromagnetic interference (EMI) shielding, 3D printedelectronics, indium tin oxide (ITO) replacements, printedpiezoresistives, bio sensors, printed memory, organic light-emittingdiode (OLED) and large area LED lighting, and large area heaters.

Commercial conductive inks can contain metals (e.g., silver) suspendedin a solution. These inks are expensive, can fail after repeatedbending, can require high temperature annealing, and have been known tolead to irritation when placed next to the skin. Newly introducedgraphitic based inks are derived from oxidized graphite, and are thusexpensive, lack long-term stability, can require damagingpost-application treatment, and do not have the high conductivity ofpristine graphene.

Flexible patterns are often produced with inks loaded with highconcentration of metals such as, for example, gold or silver. Conductivecloth can be produced by electroplating with metals such as, forexample, silver or nickel. The use of metals can be costly as well aslead to skin irritation in some cases.

Thus, an interest exists for improved conductive inks, and relatedmethods of use and fabrication. These and other inefficiencies andopportunities for improvement are addressed and/or overcome by thesystems, assemblies and methods of the present disclosure.

SUMMARY OF THE DISCLOSURE

The present disclosure provides advantageous sheet stabilized emulsionbased inks, and improved methods for fabricating and using such inks.More particularly, the present disclosure provides improved methods forfabricating conductive inks derived from water-in-oil emulsionsstabilized by sheets exfoliated from layered materials (e.g.,substantially pristine and non-oxidized graphite or hexagonal boronnitride), and related methods of use.

Research has shown that the insolubility of pristine graphene/graphitecan be utilized as a means to fabricate water/oil emulsions, withgraphene/graphite stabilizing the spheres formed, and with the emulsionsutilized as the frameworks to make composites (e.g., foam composites).See, e.g., U.S. Pat. No. 9,646,735, the entire contents of which beinghereby incorporated by reference in its entirety.

As described and disclosed in U.S. Pat. No. 9,646,735, by using aninterface trapping method, the lack of solubility of pristinegraphene/graphite can be utilized to both exfoliate and trapgraphene/graphite, as well as form stable emulsions used as theframework for polymer/graphene/graphite composites (e.g., hollowpolymer/graphene/graphite composites).

Other research has shown film climbing using an interface trappingmethod in a heptane and water mixture. See, e.g., U.S. Pat. No.9,685,261, and Woltornist, S. J., Oyer, A. J., Carrillo, J.-M. Y.,Dobrynin, A. V & Adamson, D. H., Conductive Thin Films Of PristineGraphene By Solvent Interface Trapping, ACS Nano 7, 7062-6 (2013), theentire contents of each being hereby incorporated by reference in theirentireties.

In exemplary embodiments of the present disclosure, a layered material(e.g., substantially pristine and non-oxidized graphite or substantiallypristine and non-oxidized hexagonal boron nitride) is exfoliated intoindividual sheets (e.g., individual graphene sheets), and these sheetsare utilized to stabilize water-in-oil emulsions.

In certain embodiments, by utilizing long chain alkanes (e.g.,hexadecane, which is a chain of 16 carbon atoms), one can advantageouslyfabricate emulsions with high viscosity and stability. The viscosity canbe similar to emulsions such as mayonnaise, and can also be similar tothe viscosity found in inks used for screen-printing. In this form, theemulsions can be used as inks, thereby advantageously providing aninexpensive route to printing electrically conducting and/or insulatinglines and shapes.

The present disclosure provides for a method for fabricating an inkincluding a) providing a phase separated system of two non-mixingsolvents, the phase separated system including: (i) a first solvent anda second solvent, and (ii) an interface between the first and secondsolvents; b) introducing a layered material to the interface of thephase separated system; c) forming an emulsion of the first and secondsolvents, at least a portion of the layered material stabilizing theemulsion; and d) applying the emulsion to a substrate to form anelectrically conductive pattern on the substrate.

The present disclosure also provides for a method for fabricating an inkwherein the first solvent is a long chain alkane and the second solventis water. The present disclosure also provides for a method forfabricating an ink wherein the first solvent includes at least onealkane and the second solvent is water.

The present disclosure also provides for a method for fabricating an inkwherein the layered material is substantially pristine graphite orhexagonal boron nitride; and wherein after step c) the emulsion isstabilized by layers or sheets of the substantially pristine graphite orhexagonal boron nitride.

The present disclosure also provides for a method for fabricating an inkwherein the emulsion is formed via a formation step selected from thegroup consisting of hand mixing, hand shaking, mechanical mixing,mechanical shaking, and combinations thereof. The present disclosurealso provides for a method for fabricating an ink wherein the emulsionis a water-in-oil emulsion.

The present disclosure also provides for a method for fabricating an inkwherein the emulsion is applied to the substrate via brushing or screenprinting. The present disclosure also provides for a method forfabricating an ink wherein the substrate is flexible.

The present disclosure also provides for a method for fabricating an inkwherein the first solvent is hexadecane and the second solvent is water.The present disclosure also provides for a method for fabricating an inkwherein the first solvent includes heptane and hexadecane, and thesecond solvent is water.

The present disclosure also provides for a method for fabricating an inkwherein the emulsion has a steady state viscosity of about 4,000,000 cPshear thinning to around 15,000 cP. The present disclosure also providesfor a method for fabricating an ink wherein the layered materialintroduced includes flakes, the flakes having a flake size of about 1μm. The present disclosure also provides for a method for fabricating anink wherein the layered material introduced includes graphite flakes,the graphite flakes having a flake size of about 1 μm.

The present disclosure also provides for a method for fabricating an inkwherein the first solvent includes alkanes larger than octadecane.

The present disclosure also provides for a method for fabricating an inkincluding a) providing a phase separated system of two non-mixingsolvents, the phase separated system including: (i) a first solvent anda second solvent, and (ii) an interface between the first and secondsolvents; b) introducing a layered material to the interface of thephase separated system; c) forming an emulsion of the first and secondsolvents, at least a portion of the layered material stabilizing theemulsion; and d) applying the emulsion to a substrate to form anelectrically conductive pattern on the substrate; wherein the firstsolvent is a long chain alkane and the second solvent is water; whereinthe layered material is substantially pristine graphite or hexagonalboron nitride; wherein after step c) the emulsion is stabilized bylayers or sheets of the substantially pristine graphite or hexagonalboron nitride; wherein the emulsion is formed via hand mixing; whereinthe emulsion is a water-in-oil emulsion; wherein the emulsion is appliedto the substrate via brushing or screen printing; wherein the substrateis flexible; wherein the emulsion has a steady state viscosity of about4,000,000 cP shear thinning to about 15,000 cP; and wherein the layeredmaterial introduced includes flakes, the flakes having a flake size ofabout 1 μm.

Any combination or permutation of embodiments is envisioned. Additionaladvantageous features, functions and applications of the disclosedsystems, assemblies and methods of the present disclosure will beapparent from the description which follows, particularly when read inconjunction with the appended figures. All references listed in thisdisclosure are hereby incorporated by reference in their entireties.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and aspects of embodiments are described below with referenceto the accompanying drawings, in which elements are not necessarilydepicted to scale.

Exemplary embodiments of the present disclosure are further describedwith reference to the appended figures. It is to be noted that thevarious steps, features and combinations of steps/features describedbelow and illustrated in the figures can be arranged and organizeddifferently to result in embodiments which are still within the scope ofthe present disclosure. To assist those of ordinary skill in the art inmaking and using the disclosed systems, assemblies and methods,reference is made to the appended figures, wherein:

FIG. 1 shows exemplary lines of ink printed on a substrate;

FIG. 2A depicts graphite trapped at the oil and water interface; FIG. 2Bis an illustration of graphite trapped in the oil and water interface;FIG. 2C is an illustration of graphite that exfoliates into graphene atthe oil and water interface;

FIG. 3A shows a graphene emulsion ink poured onto paper; FIG. 3B is anoptical image of the graphene emulsion ink (ink was diluted using oilphase to separate the spheres);

FIG. 3C is an illustration of a water-in-oil emulsion with graphenestabilizing the interface;

FIG. 4A displays a UCONN logo printed on paper using a graphene emulsionink;

FIG. 4B shows a plot of resistance of a printed ink line vs. the numberof cycles the ink line is rolled into a 7.62 cm diameter tube;

FIG. 5 shows different exfoliation stages of graphene ink prepared usingincreasing graphite loading from vial 1 to vial 8; all eight vials had 3ml of C16 (hexadecane), 7 ml of DI H₂O, and the graphite loading of eachvial was as follows: vial 1: 0.01 g, vial 2: 0.02 g, vial 3: 0.03 g,vial 4: 0.04 g, vial 5: 0.05 g, vial 6: 0.1 g, vial 7: 0.2 g, vial 8:0.3 g; this image shows after day one, after each vial was shaken for 40s;

FIG. 6 shows different exfoliation stages of graphene ink prepared usingincreasing graphite loading from vial 1 to vial 8; all eight vials had 3ml of C16 (hexadecane), 7 ml of DI H₂O, and the graphite loading of eachvial was as follows: vial 1: 0.01 g, vial 2: 0.02 g, vial 3: 0.03 g,vial 4: 0.04 g, vial 5: 0.05 g, vial 6: 0.1 g, vial 7: 0.2 g, vial 8:0.3 g; this image shows after day two, after each vial was shaken againfor 40 s;

FIG. 7 shows different exfoliation stages of graphene ink prepared usingincreasing graphite loading from vial 1 to vial 8; all eight vials had 3ml of C16 (hexadecane), 7 ml of DI H₂O, and the graphite loading of eachvial was as follows: vial 1: 0.01 g, vial 2: 0.02 g, vial 3: 0.03 g,vial 4: 0.04 g, vial 5: 0.05 g, vial 6: 0.1 g, vial 7: 0.2 g, vial 8:0.3 g; this image shows after day twelve, after each vial was shakenagain at day five and day twelve for 40 s;

FIG. 8 shows stress vs. shear rate at 25° C. of inks prepared by using adifferent alkane as the oil phase (C7: heptane, C10: octane, C12:dodecane; C14: tetradecane; C16: hexadecane);

FIG. 9 shows an emulsion size distribution of different inks (C7:heptane, C10: octane, C12: dodecane; C14: tetradecane; C16: hexadecane);

FIG. 10 shows the percent bleeding of lines printed using different inkson paper vs. the number of prints each line was (repeatedly) printed;(C7: heptane, C10: octane, C12: dodecane; C14: tetradecane; C16:hexadecane);

FIG. 11 shows the resistance of a 4 pt width, 5 cm length C16 ink lineversus the number of prints; and

FIGS. 12A-12E show the resistance vs. 1/(X·N) of different inks; FIG.12A is C7 ink; FIG. 12B is C10 ink; FIG. 12C is C12 ink; FIG. 12D is C14ink; FIG. 12E is C16 ink.

DETAILED DESCRIPTION OF DISCLOSURE

The exemplary embodiments disclosed herein are illustrative ofadvantageous sheet stabilized emulsion based inks, and systems of thepresent disclosure and methods/techniques thereof. It should beunderstood, however, that the disclosed embodiments are merely exemplaryof the present disclosure, which may be embodied in various forms.Therefore, details disclosed herein with reference to exemplaryinks/fabrication methods and associated processes/techniques of assemblyand use are not to be interpreted as limiting, but merely as the basisfor teaching one skilled in the art how to make and use the advantageousinks/systems and/or alternative inks/systems of the present disclosure.

The present disclosure provides improved sheet stabilized emulsion basedinks, and improved methods for fabricating and using such inks. Moreparticularly, the present disclosure provides advantageous methods forfabricating conductive inks derived from water-in-oil emulsionsstabilized by sheets exfoliated from layered materials (e.g.,substantially pristine and non-oxidized graphite or hexagonal boronnitride), and related methods of use.

Exfoliated sheets such as, for example, graphene or hexagonal boronnitride can be utilized to stabilize water-in-oil emulsions. Usingcertain oil phases, these emulsions can be very stable, lasting formonths and displaying viscosities similar to mayonnaise. In certainembodiments, by utilizing long chain alkanes (e.g., hexadecane, which isa chain of 16 carbon atoms), one can advantageously fabricate emulsionswith high viscosity and stability. In this form, the emulsions can beused as inks, thereby advantageously providing an inexpensive route toprinting electrically conducting and/or insulating lines and shapes.

The inks can be applied with a brush, by screen printing, or othertechniques (e.g., sprayed; ink-jetted; etc.) to produce conductivepatterns on flexible surfaces such as, for example, cloth or plastic.Applications of such inks can include, without limitation, wearableelectronics, flexible displays, bendable energy storage devices, androll to roll produced solar cells.

In certain embodiments, the conductive ink is fabricated by exfoliatinga layered material (e.g., substantially pristine and non-oxidizedgraphite) into individual sheets (e.g., individual graphene sheets), andusing these sheets to stabilize water-in-oil emulsions. Thisstabilization is a result of kinetic trapping of graphene sheets orseveral layers of graphene flakes at a solvent/solvent interface. Inexemplary embodiments, the systems/methods of the present disclosureadvantageously produce emulsions of graphene/graphite with liquids(e.g., two non-mixing solvents, such as oil and water) on both theinside and the outside of the graphene/graphite.

In general, fabrication of the sheet stabilized emulsion based inksbegins with a layered material (e.g., substantially pristine andnon-oxidized graphite, such as graphene sheets or layers of graphite)being placed at the interface of a phase separated system (e.g., at aninterface of two non-mixing solvents, such as a alkane/water system). Inthe interface trapping method, exfoliated sheets are instantly adsorbedto the high-energy liquid-liquid interface, where they are trappedbecause of the lowering of the interfacial energy of the system that thesheet provides. As more sheets are exfoliated, they climb up theinterface to continue to minimize the interfacial energy as much aspossible.

In order to continue the interfacial energy minimization, spheres areformed, thereby creating more surface area for the sheets (e.g.,graphene/graphite sheets) to adsorb on to. The resulting emulsion can beutilized as a conductive ink (e.g., applied to a substrate to form anelectrically conductive pattern on the substrate).

In one specific oil/water system, the emulsion consists of spheres ofwater, coated with graphene, and surrounded by at least one alkane(e.g., a long chain alkane; a high molecular weight (MW) alkane).

FIG. 1 shows exemplary lines 12 of ink printed on a substrate 10 (e.g.,artificial leather; paper, etc.). As such, FIG. 1 illustrates someprinted lines 12 of ink onto artificial leather 10. These lines 12 areelectrically conductive, even when the substrate 10 is bent or twisted.

Printable inks can allow for the development of flexible electronics onvarious substrates 10 (e.g., paper or plastic). This in turn can enableapplications such as, for example, wearable medical sensors, antennas,and even batteries and displays. The applicability of the advantageousinks of the present disclosure to screen-printing is important, as thiscan be the approach of choice for commercial printing (as opposed to theink jet printing approach).

In exemplary embodiments, layered materials (e.g., graphite or hexagonalboron nitride) are exfoliated without the need for expensive or damagingapproaches. By using long chain alkanes for the oil phase to stabilizethe emulsions against coalescence, the advantageous emulsions can befabricated. Using these emulsions, one can utilize them with standardscreen printing to create/fabricate electrically conductive lines onsubstrates (e.g., paper, fabric, etc.).

It is noted that other approaches to using graphene in inks rely oneither expensive and damaging oxidation or mechanical exfoliation.Oxidation creates defect sites on the graphene sheets that lowers theconductivity and leads to chemically unstable materials, whilemechanical methods break the sheets into small fragments and degradedproperties. In exemplary embodiments, the exfoliation systems andmethods of the present disclosure advantageously produce large graphenesheets (e.g., about 1 μm sheets) in substantially pristine or pristinecondition with negligible cost.

As described in U.S. Patent Pub. No. 2015/0307730 (the '730publication), this publication attempts to provide a graphene ink fromun-oxidized graphene. In an attempt to work, the formulation includes ahydrophobic solvent and a stabilizer, with ethyl cellulose being thestabilizer. The hydrocarbon described includes hexane, heptane, octane.The '730 publication reports attempting to exfoliate the graphite withsonication and the preponderance of very small (tens of nanometers)graphene flakes. By comparison, exemplary systems/methods of the presentdisclosure utilize water and a high MW alkane, do not requiresonication, and contain/provide larger (e.g., about 1 μm sheets), andthus more conductive, graphene. In addition, the exemplary methods ofthe present disclosure do not require a dispersing agent as does the'730 publication.

It is noted that FIG. 2A of the present disclosure depicts graphitetrapped at the oil and water interface. FIG. 2B is an illustration ofgraphite trapped in the oil and water interface. FIG. 2C is anillustration of graphite that exfoliates into graphene at the oil andwater interface.

FIG. 3A shows a graphene emulsion ink poured onto paper. FIG. 3B is anoptical image of the graphene emulsion ink (ink was diluted using oilphase to separate the spheres). FIG. 3C is an illustration of awater-in-oil emulsion with graphene stabilizing the interface.

FIG. 4A displays a UCONN logo printed on paper using a graphene emulsionink. FIG. 4B shows a plot of resistance of a printed ink line versus thenumber of cycles the ink line is rolled into a 7.62 cm diameter tube.

FIG. 5 shows different exfoliation stages of graphene ink prepared usingincreasing graphite loading from vial 1 to vial 8. All eight vials had 3ml of C16 (hexadecane), 7 ml of DI H₂O, and the graphite loading of eachvial was as follows: vial 1: 0.01 g, vial 2: 0.02 g, vial 3: 0.03 g,vial 4: 0.04 g, vial 5: 0.05 g, vial 6: 0.1 g, vial 7: 0.2 g, vial 8:0.3 g; this image shows after day one, after each vial was shaken for 40seconds.

FIG. 6 shows different exfoliation stages of graphene ink prepared usingincreasing graphite loading from vial 1 to vial 8. All eight vials had 3ml of C16 (hexadecane), 7 ml of DI H₂O, and the graphite loading of eachvial was as follows: vial 1: 0.01 g, vial 2: 0.02 g, vial 3: 0.03 g,vial 4: 0.04 g, vial 5: 0.05 g, vial 6: 0.1 g, vial 7: 0.2 g, vial 8:0.3 g; this image shows after day two, after each vial was shaken againfor 40 seconds.

FIG. 7 shows different exfoliation stages of graphene ink prepared usingincreasing graphite loading from vial 1 to vial 8. All eight vials had 3ml of C16 (hexadecane), 7 ml of DI H₂O, and the graphite loading of eachvial was as follows: vial 1: 0.01 g, vial 2: 0.02 g, vial 3: 0.03 g,vial 4: 0.04 g, vial 5: 0.05 g, vial 6: 0.1 g, vial 7: 0.2 g, vial 8:0.3 g; this image shows after day twelve, after each vial was shakenagain at day five and day twelve for 40 seconds.

FIG. 8 shows stress versus shear rate at 25° C. of inks prepared byusing a different alkane as the oil phase (C7: heptane, C10: octane,C12: dodecane; C14: tetradecane; C16: hexadecane).

FIG. 9 shows an emulsion size distribution of different inks (C7:heptane, C10: octane, C12: dodecane; C14: tetradecane; C16: hexadecane).

FIG. 10 shows the percent bleeding of lines printed using different inkson paper versus the number of prints each line was (repeatedly) printed(C7: heptane, C10: octane, C12: dodecane; C14: tetradecane; C16:hexadecane).

FIG. 11 shows the resistance of a 4 pt width, 5 cm length C16 ink lineversus the number of prints.

FIGS. 12A-12E show the resistance versus 1/(X·N) of different inks. FIG.12A is C7 ink. FIG. 12B is C10 ink. FIG. 12C is C12 ink. FIG. 12D is C14ink. FIG. 12E is C16 ink.

Table 1 below shows the hysteresis of different alkanes with graphene.

TABLE 1 average average advancing weight receding weight solvent gain(mg) retained (mg) hysteresis C7 32.6 37.7 0.157 C10 39.5 44.8 0.133 C1241.3 43.9 0.064 C14 45.7 45.8 0.001 C16 40.2 45.1 0.120

With Equation 1:

$R = {\frac{1}{X \times N}R_{0}}$

And where:

-   -   R: resistance of the printed line (Me)    -   X: Width of the line (pt)    -   N: Number of prints on the same line    -   R₀: resistance per print per points of the line        (MΩ·print⁻¹·pt⁻¹)

Table 2 below shows the Resistance per print per points (R₀) ofdifferent inks and the coefficient of determination (R²) of differentinks.

TABLE 2 Ink R₀ (MΩ · print⁻¹ · pt⁻¹) R² C7 ink 19.57 0.35 C10 ink 28.910.84 C12 ink 64.97 0.72 C14 ink 44.17 0.58 C16 ink 124.18 0.95

The present disclosure will be further described with respect to thefollowing examples; however, the scope of the disclosure is not limitedthereby. The following examples illustrate the advantageoussystems/methods of the present disclosure of fabricating improvedconductive inks derived from water-in-oil emulsions stabilized by sheetsexfoliated from layered materials.

Example 1

An exemplary sample of ink can be produced/fabricated by adding graphiteflakes to water and hexadecane (e.g., three to one ratio of water tohexadecane in some embodiments; nearly equal volumes of water andhexadecane in other embodiments). This mixture is then mixed or shaken(e.g., via hand mixing, hand shaking, mechanical mixing, mechanicalshaking, and combinations thereof) for an amount of time (e.g., for lessthan ten seconds) to produce the emulsion/ink. That is it.

The ink is stable to coalescence relative to the length of timeinvestigating it (e.g., substantially no coalescence observed for morethan three months). The mayonnaise-like consistency (e.g., about 15,000cP, but can be varied; in some embodiments the emulsion has a steadystate viscosity of about 4,000,000 cP shear thinning to about 15,000 cP)of the ink is perfect for screen printing, and numerous printed designshave been fabricated.

Current research is concerned with exploring the use of differentalkanes and ratios of alkanes, as well as different graphite flakesizes.

An initial alkane utilized in the fabrication method was C16(hexadecane). Current tests include inks made with various ratios of C16and C7 (heptane) during the fabrication method.

Some findings thus far are that the C16 can be cut with C7 to asignificant extent without losing the high viscosity of the resultantink/emulsion.

With just only C7, however, the emulsion flows freely. In addition, onecan test graphene with larger flake sizes.

Some embodiments utilize around 1 μm flakes (1 μm equals 1,000nanometers). This is due the fast exfoliation of this size flake. Largerflakes, however, are expected to be more conductive, and one can utilizemixing techniques and/or microwaves in efforts to make inks with largerflakes in a reasonable amount of time.

Another direction one can take is to utilize longer alkanes (e.g.,larger than C18, octadecane) with higher melting temperatures. These aretypically called waxes, and should be able to form emulsions either atelevated temperatures or when cut with C7. If one is able to use waxeswith high melting temperatures in the emulsification process, thenremove the water and C7, one may be able to make very low densityconductive pastes. These approaches can lead to the control of viscosityand rheological properties of the ink, and provide a pathway for meetinga range of industrial needs.

In printing applications, it has been noted that the conductivity of thelines 12 increases with multiple prints. This is important forunderstanding the mechanism, but also for allowing for changingconductivity on the same surface/substrate. This is an aspect that moreexpensive silver based inks lack, and is useful for various applicationswhere the material interacts with electromagnetic waves.

Some future objectives of the present disclosure are to more fullyunderstand the source of emulsion stability in these exemplary inks, todevelop additional formulations and approaches to manufacture such inks,and to provide additional examples and test samples for use/testing.

Whereas the disclosure has been described principally in connection withgraphite and/or graphene, such description has been utilized forpurposes of disclosure and is not intended as limiting the disclosure.To the contrary, it is recognized that the disclosed systems, methods,techniques and assemblies are capable of use with other materials havinga layered structure or the like, such as, for example, boron nitride(e.g., hexagonal or graphitic boron nitride) or graphene oxide or thelike.

Although the systems and methods of the present disclosure have beendescribed with reference to exemplary embodiments thereof, the presentdisclosure is not limited to such exemplary embodiments and/orimplementations. Rather, the systems and methods of the presentdisclosure are susceptible to many implementations and applications, aswill be readily apparent to persons skilled in the art from thedisclosure hereof. The present disclosure expressly encompasses suchmodifications, enhancements and/or variations of the disclosedembodiments. Since many changes could be made in the above constructionand many widely different embodiments of this disclosure could be madewithout departing from the scope thereof, it is intended that all mattercontained in the drawings and specification shall be interpreted asillustrative and not in a limiting sense. Additional modifications,changes, and substitutions are intended in the foregoing disclosure.Accordingly, it is appropriate that the appended claims be construedbroadly and in a manner consistent with the scope of the disclosure.

What is claimed is:
 1. A method for fabricating an ink comprising: a)providing a phase separated system of two non-mixing solvents, the phaseseparated system including: (i) a first solvent and a second solvent,and (ii) an interface between the first and second solvents; b)introducing a layered material to the interface of the phase separatedsystem; c) forming an emulsion of the first and second solvents, atleast a portion of the layered material stabilizing the emulsion; and d)applying the emulsion to a substrate to form an electrically conductivepattern on the substrate.
 2. The method of claim 1, wherein the firstsolvent is a long chain alkane and the second solvent is water.
 3. Themethod of claim 1, wherein the first solvent includes at least onealkane and the second solvent is water.
 4. The method of claim 1,wherein the layered material is substantially pristine graphite orhexagonal boron nitride; and wherein after step c) the emulsion isstabilized by layers or sheets of the substantially pristine graphite orhexagonal boron nitride.
 5. The method of claim 1, wherein the emulsionis formed via a formation step selected from the group consisting ofhand mixing, hand shaking, mechanical mixing, mechanical shaking, andcombinations thereof.
 6. The method of claim 1, wherein the emulsion isa water-in-oil emulsion.
 7. The method of claim 1, wherein the emulsionis applied to the substrate via brushing or screen printing.
 8. Themethod of claim 1, wherein the substrate is flexible.
 9. The method ofclaim 1, wherein the first solvent is hexadecane and the second solventis water.
 10. The method of claim 1, wherein the first solvent includesheptane and hexadecane, and the second solvent is water.
 11. The methodof claim 1, wherein the emulsion has a steady state viscosity of about4,000,000 cP shear thinning to about 15,000 cP.
 12. The method of claim1, wherein the layered material introduced includes flakes, the flakeshaving a flake size of about 1 μm.
 13. The method of claim 1, whereinthe layered material introduced includes graphite flakes, the graphiteflakes having a flake size of about 1 μm.
 14. The method of claim 1,wherein the first solvent includes alkanes larger than octadecane. 15.The method of claim 1, wherein the layered material is substantiallypristine and non-oxidized graphite or hexagonal boron nitride; andwherein after step c) the emulsion is stabilized by layers or sheets ofthe substantially pristine and non-oxidized graphite or hexagonal boronnitride.
 16. The method of claim 1, wherein the emulsion is applied tothe substrate via spraying or ink-jetting.
 17. A method for fabricatingan ink comprising: a) providing a phase separated system of twonon-mixing solvents, the phase separated system including: (i) a firstsolvent and a second solvent, and (ii) an interface between the firstand second solvents; b) introducing a layered material to the interfaceof the phase separated system; c) forming an emulsion of the first andsecond solvents, at least a portion of the layered material stabilizingthe emulsion; and d) applying the emulsion to a substrate to form anelectrically conductive pattern on the substrate; wherein the firstsolvent is a long chain alkane and the second solvent is water; whereinthe layered material is substantially pristine and non-oxidized graphiteor hexagonal boron nitride; wherein after step c) the emulsion isstabilized by layers or sheets of the substantially pristine andnon-oxidized graphite or hexagonal boron nitride; wherein the emulsionis formed via hand mixing; wherein the emulsion is a water-in-oilemulsion; wherein the emulsion is applied to the substrate via brushingor screen printing; wherein the substrate is flexible; wherein theemulsion has a steady state viscosity of about 4,000,000 cP shearthinning to about 15,000 cP; and wherein the layered material introducedincludes flakes, the flakes having a flake size of about 1 μm.